Conventionally, in consideration of the rapidity of chemical reactions, and the need to carry out reactions using very small amounts, on-site analysis and the like, integration technology for carrying out chemical reactions in very small spaces has been focused upon, and research into this technology has been carried out with vigor throughout the world.
Microchemical systems that use glass substrates or the like are an example of such integration technology for carrying out chemical reactions. Such a microchemical system is intended to have capability of carrying out all functions of mixing, reaction, separation, extraction, detection or the like on a sample placed in a very narrow channel which is formed in a small glass substrate or the like. Examples of reactions carried out in the microchemical system include diazotization reactions, nitration reactions, and antigen-antibody reactions. Examples of extraction/separation include solvent extraction, electrophoretic separation, and column separation.
As an example in which ‘separation’ is the sole aim, an electrophoresis apparatus for analyzing extremely small amounts of proteins, nucleic acids or the like has been proposed by Japanese Laid-open Patent Publication (Kokai) No. 8-178897. This electrophoresis apparatus analyzes extremely small amounts of proteins, nucleic acids or the like and is provided with a channel-formed plate-shaped element comprised of two glass substrates joined together. Because the element is plate-shaped, breakage is less likely to occur than in the case of a glass capillary tube having a circular or rectangular cross section, and hence handling is easier.
In these microchemical systems, because the amount of the sample is very small, a high-precision detection method is essential. The path to making a detection method of the required precision fit for practical use has been opened up through the establishment of a photothermal conversion spectroscopic analysis method which utilizes a thermal lens effect that is produced through a liquid-borne sample absorbing light in a very narrow channel.
The photothermal conversion spectroscopic analysis method utilizes a photothermal conversion effect that when light is convergently irradiated onto a sample, the temperature of a solvent is locally increased by thermal energy emitted due to light absorbed by a solute in the sample to cause a change in the refractive index and hence generate a thermal lens.
FIG. 7 is a view useful in explaining the principle of a thermal lens.
In FIG. 7, a convergent beam of exciting light is irradiated onto an extremely small sample via an objective lens of a microscope, whereupon the photothermal conversion effect described above takes place. For most substances, the refractive index drops as the temperature rises, and hence the drop rate of the refractive index of the sample is greater toward the center of the convergent beam of exciting light, which is where the temperature rise is highest. Due to thermal diffusion, the temperature rise becomes smaller and hence the drop in refractive index becomes smaller, with increasing distance from the center of the convergent beam of exciting light, i.e. decreasing distance to the periphery of the same. Optically, this pattern of change in the refractive index brings about the same effect as with a concave lens, and hence the effect is called the thermal lens effect. The size of the thermal lens effect, i.e. the power of the thermal lens is proportional to the optical absorbance of the sample. Moreover, in the case that the refractive index increases with temperature, a converse effect to the above, i.e. the same effect as a convex lens is produced.
In the photothermal conversion spectroscopic analysis method described above, thermal diffusion in a sample, i.e. change in refractive index of the sample, is observed, and hence the method is suitable for detecting concentrations in extremely small amounts of samples.
A photothermal conversion spectroscopic analyzer has been proposed by Japanese Laid-open Patent Publication (Kokai) No. 10-232210 as a microchemical system that uses the photothermal conversion spectroscopic analysis method described above.
In the conventional photothermal conversion spectroscopic analyzer, a channel-formed plate-shaped element is disposed below the objective lens of a microscope, and exciting light of a predetermined wavelength outputted from an exciting light source is introduced into the microscope. The exciting light is thus convergently irradiated via the objective lens onto a sample in the analysis channel of the channel-formed plate-shaped element. Thus, a thermal lens is formed about the convergent irradiation position in which the exciting light is convergently irradiated.
Moreover, detecting light having a wavelength different to that of the exciting light is outputted from a detecting light source and also introduced into the microscope and then emitted therefrom. The detecting light emitted from the microscope is convergently irradiated onto the thermal lens that has been formed in the sample by the exciting light. Then, the detecting light passing through the sample is either diverged or converged due to the effect of the thermal lens. The diverged or converged light exiting the sample passes as signal light through a converging lens and a filter or just a filter, and is then received and detected by a detector. The intensity of the detected signal light depends on the refractive index of the thermal lens formed in the sample. The detecting light may have the same wavelength as that of the exciting light, or the exciting light may be used as the detecting light as well.
In the spectroscopic analyzer described above, a thermal lens is thus formed at the convergent irradiation position (hereinafter referred to as “the focal position”) of the exciting light, and the change in refractive index within the formed thermal lens is detected by means of detecting light.
In most cases where the photothermal conversion spectroscopic analysis method using the thermal lens described above is carried out, it is required that the focal position of the exciting light and that of the detecting light should be different from each other. FIGS. 8A and 8B are views useful in explaining the formation position of the thermal lens and the focal position of the detecting light in the direction of travel of the exciting light. FIG. 8A shows a case in which the objective lens has chromatic aberration, whereas FIG. 8B shows a case in which the objective lens does not have chromatic aberration.
In the case that the objective lens 130 has chromatic aberration, a thermal lens 131 is formed at the focal position 132 of the exciting light as shown in FIG. 8A. The focal position 133 of the detecting light is shifted by an amount ΔL from the focal position 132 of the exciting light, and thus changes in the refractive index within the thermal lens 131 can be detected as changes in the focal distance of the detecting light from the detecting light. In the case that the objective lens 130 does not have chromatic aberration, on the other hand, the focal position 133 of the detecting light is almost exactly the same as the focal position 132 of the exciting light, i.e. the position of the thermal lens 131 as shown in FIG. 8B. The detecting light is thus not deflected by the thermal lens 131, and hence changes in the refractive index within the thermal lens 131 cannot be detected.
However, the objective lens of a microscope is generally manufactured so as not to have chromatic aberration, and hence the focal position 133 of the detecting light is almost exactly the same as the position of the thermal lens 131 formed at the focal position 132 of the exciting light as described above, as shown in FIG. 8B. Changes in the refractive index within the thermal lens 131 thus cannot be detected. There is thus a problem that trouble must be taken to either shift the position in which the thermal lens 131 is formed from the focal position 133 of the detecting light every time a measurement is taken as shown in FIGS. 9A and 9B, or else angle the detecting light slightly using a lens (not shown) before passing the detecting light through the objective lens 130 so that the focal position 133 of the detecting light will be shifted from the thermal lens 131 as shown in FIG. 10. This also leads to degraded working efficiency of the user.
It is an object of the present invention to provide a microchemical system which enables working efficiency of the user to be improved and can be made smaller in size.